An attenuator (for example, a voltage controlled attenuator) is an element applied in a microwave system, and is used for attenuating signal power, so as to control and adjust the output power of the system. If a base station transmits signals at 40 W, the base station can generally cover a circular area with a radius of 2 Km. When the base station detects that a receiving terminal (for example, a mobile phone) is 2 Km away from the base station, the base station transmits signals at full power (that is, 40 W), so that the receiving terminal can receive the signals from the base station. When the base station detects that the receiving terminal is close, for example, only 100 m away from the base station, the base station can reduce the transmission power by adopting an attenuator, for example, the base station can communicate with the receiving terminal by transmitting signals at 2 W, so as to prevent the receiving terminal from being burned out due to excessively high input power.
As shown in FIG. 1, a voltage controlled attenuator in the prior art includes a 3 dB bridge and two PIN diodes.
In the implementation of the present invention, the inventors found that the attenuator in the prior art at least has the following defects.
A voltage-controlled source Vg controls the resistance of the PIN diodes. When the resistance of the PIN diodes is 50Ω, maximum attenuation is achieved. If the resistance of the PIN diodes is near 50Ω, the resistance easily changes slightly due to the device process or high/low temperature, which accelerates variation of the attenuation. The circuit is very sensitive, and the unstable variation of the attenuation results in poor reliability of the circuit.